Critical review of the nomenclature and taxonomy of Sorghastrum canescens (Poaceae: Panicoideae: Andropogoneae), an endemic Brazilian species

Some taxonomic groups impose the need to use continuous morphological characteristics in taxon delimitation, and the grass genus Sorghastrum is a clear case of this necessity. Sorghastrum canescens was described based on the length of its awns. However, insufficient and scattered sampling has obscured the identity of this species for at least 137 years, while it was considered synonym of S. incompletum var. incompletum. In this study we evaluate statistical differences in the original and current morphological concepts of S. canescens using analysis of variance and posterior pairwise comparison of means and medians. We also retrieved the nomenclatural history of the binomial S. canescens to clarify possible errors in the synonymization of this species. All the statistical evidence refutes the hypothesis that S. canescens is a synonym of S. incompletum var. incompletum. Historical data revealed an error in the identification of the correct basionym of S. canescens and this error has been repeated in several taxonomic revisions. We were also able to establish an approximate date for the type-collection of S. canescens. We therefore propose the reestablishment of the name Sorghastrum canescens and provide morphological descriptions and illustration of this species.